1. Field of the Invention
The present invention relates to a composition for a non-wettable coating, and to a process for applying it to a substrate. It applies preferentially to a substrate of this type which is transparent; in this regard, it therefore relates in particular to the manufacture of glazing provided with a non-wettable coating.
2. Description of the Background
The glazing relevant to the invention is glazing made of glass and/or plastic such as poly(methyl methacrylate) (PMMA), polyvinyl butyral (PVB), polycarbonate (PC) or polyurethane (PU). This glazing is used, in particular, in the aeronautical, railway or automotive fields. It can also be used in the building field or in the field of household fittings, for example for decorative panels, furniture, household electrical appliances (refrigerator and oven doors, windows) etc.
The wettability nature which is referred to pertains to the fact that polar or non-polar liquids adhere to the substrate and form an undesirable film. The term wettability is also used to describe the tendency of substrates to retain dust or dirt of all kinds, finger marks, insects, etc.
The presence of water and/or dirt gives an unattractive appearance, may reduce the transparency of the substrate, and may obscure vision through it. The latter points are particularly problematic when the substrate is glazing used in the field of transport.
The non-wettability of a substrate, more commonly referred to as its hydrophobic/oleophobic property, consists in the fact that the contact angles between a liquid and this substrate are high, for example at least 90xc2x0 for water. The liquid therefore tends to flow readily over the substrate, in the form of drops, simply under gravity if the substrate slopes, or under the effect of aerodynamic forces in the case of a moving vehicle. Examples of agents which are known to impart this hydrophobic/oleophobic property are fluorinated alkylsilanes as described in patent applications EP 0 492 417, EP 0 492 545 and EP 0 672 779. According to these documents, the way in which this layer is obtained is that a solution containing fluorinated organosilanes in a non-aqueous organic solvent is applied to the surface of a substrate. As the non-aqueous organic solvent, document EP 0 492 545 cites, in particular, n-hexadecane, toluene, xylene, etc. These solvents are particularly suitable for a fluorinated chlorosilane. According to this document, it is also possible to use a methyl or ethyl alcohol as solvent when the fluorinated silane is a fluorinated alkoxysilane.
Particular examples of common hydrophobic/oleophobic agents are alkyl-trihalo- or -trialkoxy-silanes whose alkyl group includes at least one end that is perfluorinated, that is to say consisting of an F3Cxe2x80x94(CF2)xe2x80x94n functional group, in which n is a positive integer or zero. For these, patent application EP 0 719 743 indicates perfluoro carbons as suitable solvents.
The hydrophobic/oleophobic agents are applied in known fashion in solution using conventional deposition methods, with or without heating.
Preparation of the substrate by a prior treatment using a primer of the tetrahalo- or tetralkoxy-silane type is also known and described, amongst others in application EP 0 484 746. The purpose of this is to improve the adhesion of the hydrophobic/oleophobic coating to the substrate.
One of the problems which arises most acutely in the field of the invention is that of the hydrophobic/oleophobic coating""s erosion. This erosion takes place to a varying degree during the operations of cleaning the substrate, which it is essential to carry out occasionally, in particular to restore satisfactory vision through a transparent substrate. Constant attempts are therefore being made to slow down the progressive removal of the aforementioned types of hydrophobic/oleophobic coatings, which occurs in particular under the action of windscreen wipers. Furthermore, this type of removal may also result from degradation by ultraviolet radiation.
The inventors have succeeded in creating a hydrophobic/oleophobic coating which is especially suited to inorganic or organic transparent substrates, i.e. substrates made of glass or plastic, this coating being distinguished by excellent bonding and abrasion-resistance properties.
To this end, the invention relates to a composition for a hydrophobic/oleophobic coating which is characterized in that it contains simultaneously at least one alkoxysilane and at least one halosilane, each having a perfluorinated group at at least one end of their molecule.
Advantageously, the alkoxysilane and halosilane respectively satisfy the following formulae (I) and (II): 
in which:
m and mxe2x80x2, which are identical or different, are between 0 and 15, preferably between 4 and 10, and particularly preferably, are both equal to 7;
n and nxe2x80x2, which are identical or different, are between 1 and 5, preferably between 1 and 3 and, in particular, identical and equal to 2;
p and pxe2x80x2 have the value 0, 1 or 2 and are preferably zero;
R is an alkyl group, in particular methyl, ethyl or propyl, the first two groups mentioned being preferred;
Rxe2x80x2 and Rxe2x80x3 each represent an alkyl group or a hydrogen atom;
X is a halogen atom, preferably chlorine.
In the particularly favourable case when the two compounds which coexist in the composition of the invention are a trialkoxysilane and a trihalosilane, that is to say when p=pxe2x80x2=0, the most abrasion-resistant hydrophobic/oleophobic coatings were obtained for comparable molar concentrations of the two silanes. In this embodiment of the invention, a molar ratio of the alkoxysilane to the halosilane of between 80:20 and 20:80, or advantageously between 60:40 and 40:60, is therefore recommended.
The invention furthermore relates to the following:
1) a process for forming a hydrophobic/oleophobic coating on a substrate, which comprises the steps consisting in:
cleaning the substrate,
preferably applying a primer, such as one comprising a silane having three or four hydrolysable functional groups,
applying a composition according to the invention, and
subjecting the system to a heat treatment, this operation being optional;
2) a ready-to-use kit for hydrophobic/oleophobic treatment, consisting of a receptacle containing a composition as described above, and not requiring the separate addition of any catalyst or auxiliary treatment agent (the possibility of forming the coating by application of a single composition is of obvious practical benefit to the user, and constitutes one of the major advantages provided by the invention);
3) a substrate on which a hydrophobic/oleophobic coating has been formed from a composition according to the invention; and
4) monolithic, laminated or multiple glazing of which at least one outer glass or plastic face is at least in part provided with a hydrophobic/oleophobic coating formed from a composition according to the invention.
As regards this last subject of the invention:
xe2x80x9cmonolithic glazingxe2x80x9d means glazing consisting of a single pane of glass or sheet of plastic such as polycarbonate, poly(methyl methacrylate), etc.;
xe2x80x9claminated glazingxe2x80x9d means a stack of several panes or sheets bonded to one another, for example panes of glass or sheets of plastic fixed to one another by means of adhesive layers made of polyvinyl butyral, polyurethane, etc.; and
xe2x80x9cmultiple glazingxe2x80x9d means a combination of sheets or panes that are unconnected, that is to say in particular separated from one another by layers of air.
In the context of the invention, xe2x80x9couter facexe2x80x9d of the glazing means a surface in contact with the surrounding atmosphere. This may be the surface of a window of a motor vehicle or a building that may come into contact with rain or organic liquids, or alternatively a shower window or the like, etc.
Other characteristics and advantages of the invention will become apparent from the following examples: